Research On Low Frequency Narrow Beam Quasi-periodic Structure Transducer

Transducer has been applied in many fields,such as atomizer,ultrasonic material processing,ultrasonic probe in medical treatment,sonar in underwater communication,and so on.The sound wave is generated by the vibration of transducer chip,which can used for underwater exploration.Generally,the narrower the beam width of sound wave,the more concentrated the sound field energy.Therefore,the design of transducer with narrow beam has a good effect on improving the range and accuracy of underwater detection and improving the resolution of imaging.In order to solve the problem of the small size of the sandwich transducer at low frequency,a quasi-periodic structure transducer is proposed in this paper.The quasi-periodic structure transducer is to replace some piezoelectric pieces in the piezoelectric ceramic stack of the sandwich transducer with non-piezoelectric material.Piezoelectric ceramic pieces and non-piezoelectric materials are alternately arranged to form a quasi-periodic structure,and the polarization direction of adjacent piezoelectric ceramic piece is opposite.Lower frequency transducers can be obtained by selecting suitable non-piezoelectric material.A thin circular plate is added to the radiation end of the quasi-periodic structure transducer,because the thickness of the thin circular plate is far less than the diameter,when the longitudinal vibration of the transducer is transmitted to the thin circular plate,it will produce bending vibration,which changes the vibration velocity distribution of radiation surface of the transducer,thereby controlling the directivity opening angle of the sound field radiated by the transducer.By adjusting the diameter of the thin circular plate,the transmission voltage response and beam width at the resonance frequency of the transducer are controlled to achieve a small-sized underwater acoustic transducer with narrow beam at low frequency.The proposed transducer is analyzed by the equivalent circuit method and the finite element method,and the transducer prototype is made according to the numerical simulation results.The chief study contents and innovation points of this article are as below:1.The structure of the quasi-periodic structure transducer is designed,and the equivalent circuit theory is used to derive the equivalent circuit of the quasi-periodic structure transducer.The whole equivalent circuit and frequency equation of the quasi-periodic structure transducer are obtained without considering the loss,choose different non-piezoelectric materials,calculate the resonance frequency of the transducer,and compare with the resonance frequency of the sandwich piezoelectric transducer under the same size.The calculation formula of directivity of the radiated sound field of the low-frequency narrow-beam quasi-periodic structure transducer is derived,the diameter of the thin circular plate is changed,and the change pattern of the directivity is analyzed.2.The finite element model of quasi-periodic structure transducer is established,and the vibration modes of the transducer under different non-piezoelectric materials are analyzed,and compared with the frequency characteristics of the sandwich piezoelectric transducer under the same size.The simulation results show that the transducer with different resonance frequencies can be obtained by choosing different non-piezoelectric materials,and the resonance frequency of the quasi-periodic structure transducer is lower when the non-piezoelectric material is nylon.The finite element model of the low-frequency narrow-beam quasi-periodic structure transducer in water is established.The non-piezoelectric material is nylon,the diameter of the thin circular plate is changed and analyze the influence of transducer performance.3.The physical models of sandwich piezoelectric transducer,quasi-periodic structure transducer and low-frequency narrow-beam quasi-periodic structure transducer are made.The performance of the transducer is tested by impedance analyzer and laser doppler vibrometer,and the experimental results are compared with the equivalent circuit calculation results and finite element simulation results.